This invention relates to improvements in the back pressure hole for a scroll compressor.
Scroll compressors are becoming widely utilized in many compression applications. A scroll compressor typically includes fixed and orbiting scrolls having generally spiral wraps that interfit to define moving compression chambers.
Fluid pressure due to the compressed gas tends to force the orbiting scroll away from the fixed scroll. The prior art has tapped pressurized fluid to a chamber behind the orbiting scroll to create a force to bias the orbiting scroll back against the fixed scroll. In the prior art, the back pressure tap has typically utilized a series of interconnected small passages to tap fluid from a compression chamber through a crossing passage, through a back pressure hole and into a back pressure chamber behind the orbiting scroll. The passages have typically been formed by drilling or boring the passages into the orbiting scroll.
Drilling the back pressure hole has resulted in burrs at the end of the passage which extends through the rear of the orbiting scroll. To provide proper operation it is important that a rear face of the orbiting scroll be as smooth as possible. Thus, the provision of the back pressure hole through the rear of the orbiting scroll face has required a separate finishing operation to remove the burrs. It would be desirable to minimize the necessary manufacturing steps for manufacturing a scroll compressor, including eliminating this separate step.
In addition, scroll compressors are typically tested upon assembly to ensure they can reach a particular pressure within a particular period of time. This final test is one designed to ensure that the scroll compressor has been properly manufactured and is properly sealing the compression chambers. If the scroll compressor does not achieve the desired pressure within a particular period of time it is deemed to be unacceptable, and is identified as scrap. In the past, otherwise acceptable scroll compressors have sometimes been identified as unacceptable with this test.
A problem with this test, and a problem with scroll compressor operation in general, is that the back pressure hole has tended to be a single small hole extending through the rear of the orbiting scroll face. The hole may be closed by the crankcase upon start up, until pressure develops within the compression chamber to bias the orbiting scroll away from the crankcase. At that point, pressure from the hole forces the orbiting scroll away from the crankcase.
In addition, there is a condition known as "start-up wobble" wherein the orbiting scroll wobbles when initially started. This is believed to be a combined factor of the forces which are normally opposed by the back pressure developing more quickly than the back pressure in the back pressure chamber does, and further partially due to the back pressure hole being closed off.
Thus, there have been some undesirable features with the prior art back pressure fluid supply.